This invention relates to integrated circuit voltage regulators, and more particularly, to integrated circuit voltage regulators that operate over a wide voltage range and exhibit large power supply rejection ratios in integrated circuits such as programmable logic device integrated circuits.
Integrated circuits contain circuitry that is powered at a variety of power supply levels. In a typical scenario, an integrated circuit may contain core logic that is powered using a relatively low power supply voltage and peripheral input-output circuitry that operates at a relatively high power supply voltage. Additional circuit functions may require other power supply voltages.
One way to satisfy the need for multiple power supply voltages on an integrated circuit is to require system designers to supply suitable power supply voltages externally. This approach requires system designers to design circuit boards in which a number of power supply voltages are routed to the power supply pins of the integrated circuit.
It is generally desirable to minimize the number of power supply pins that are used in a given design. The quantity of pins available to supply an integrated circuit with power supply voltages is limited due to considerations such as circuit real estate consumption and device complexity. Although it would be convenient to be able to add a new power supply pin for each new power supply voltage that is needed on an integrated circuit, this is generally not feasible in practice.
One way to overcome the limited number of power supply voltages that are supplied externally to an integrated circuit involves generating power supply voltages using on-chip voltage regulator circuitry. By using an on-chip voltage regulator, it is possible to generate a new power supply voltage that would otherwise not be available.
Voltage regulator circuitry may also be used on an integrated circuit to regulate externally supplied power supply voltages. This helps to ensure that the circuitry on the integrated circuit will be powered at the appropriate voltage level, even if the voltage of the external supply deviates somewhat from its nominal level.
An important figure of merit for a voltage regulator is its ability to reject power supply noise. Voltage regulators characterized by large power supply rejection ratios (PSRRs) are able to effectively filter out noise on their power supply terminals. Voltage regulators with low power supply rejection ratios tend to be susceptible to noise.
In many applications, it is important that the output of the voltage regulator be close to its power supply voltage. In a voltage regulator design with a poor output range, there is a relatively large voltage drop between the voltage regulator's power supply voltage and the voltage regulator's output. In this type of situation, it may be difficult or impossible to use the voltage regulator's output for its intended purpose. Raising the voltage regulator's power supply voltage can help address this problem, but this option is often not available because there are only a limited number of externally-supplied power supply voltages and power supply voltage pins on the integrated circuit that contains the voltage regulator. Moreover, techniques that are conventionally used to help raise the power supply rejection ratio of a voltage regulator often adversely affect the voltage regulator's output range.
It would therefore be desirable to be able to provide a voltage regulator for an integrated circuit such as a programmable logic device that exhibits a large power supply rejection ratio and a wide output voltage range.